New script for denoising linear monochannel images

[eganz]

Mike,

I was enjoying the new gradient/noise thresholds parameter method, and it was improving the results for my images.
However, now in the latest version 1.21, this functionality has disappeared.

What's up?

Eric

[Buzz]

I have been having fantastic success with MUREDenoise on my images.  I tried it today and it is repeatedly creating a regular noise pattern on the images. Has something recently changed in the base algorithm? I need to open an old project and see if, indeed, something has changed.

[mschuster]

Eric, sorry, I found a gradient/noise classifier problem, the option is removed until I find a solution. Within a pixel or two of a sharp, high contrast edge (more common in natural images) denoising tends to be a bit too conservative.

Chris, yes changes (runs faster, less roundoff error, better cycle-spin effectiveness), but should be nothing that introduces this problem. Typical cause is incorrect script parameter values. Can you provide the image in dropbox, along with parameter values? I will run the previous versions for comparison.

Thank you,
Mike

[Saad]

Hello,

I am trying out the Mure Denoise camera for my images. I use a SBIG ST8300M for narrowband imaging (30 min subs) at -15C and 0C in summers.

I have computed a gain of 0.371e- and a gaussian noise of 29.52 DN. However, the result of DEMURE seems to produce blotches in the image. It is not as smooth as it is for others in this thread. What can I do to improve this?

[mschuster]

"Smoothness" is somewhat subjective and also somewhat a function of how much you stretch.

Your detector gain and noise values seem reasonable for unbinned 8300.

A couple things to try:

Double check the Image Combination count and Interpolation method settings. Incorrect values cause trouble.

Double check the Detector Offset setting. The default 0 is appropriate only for calibrated images (bias and/or dark subtracted). If the image has not been bias/dark subtracted, then a non-zero value must be used. The DarkBiasNoiseEstimator script can provide an estimate (when run on a bias or dark frame).

Try reducing the Variance scale value from default 1 to 0.9 or less. A value less than 1 will reduce the amount of denoising.

[troypiggo]

I notice that the number of interpolation algorithms in the script's drop-down do not match all of the options that star alignment.  eg Bicubic spline is available, but SA has bicubic spline and bicubic b-spline and so on.  I've been using b-spline is SA.  Results using just bicubic spline as closest match in Mure Denoise appear ok.  Just curious if that's right, or should we limit use of SA algorithms to match the options in MureDN?

[mschuster]

Troy, what you are doing is fine. When using any of the missing methods, check for excessive denoising artifacts (eg, pixel checker-boarding) and reduce Variance Scale slightly if you see problems. Sorry for the lack of support, I didn't spend the necessary development time thinking that these other methods were not often used.

[troypiggo]

Thanks mate.

[mschuster]

MureDenoise 1.22 release, should appear as an auto-update soon.

When you apply several processes to a preview, the preview's base image is normally used as input to each process. The results from previous processes are normally discarded, unless you use the command Preview > Store.

Up until this new release, MureDenoise did not work this way. If you applied MureDenoise multiple times to a preview (say to test different parameter settings) previous results were not discarded and you ended up denoising a previously denoised result, a bad thing to do. The new release fixes this problem. Thank you ngc1535 very much for finding and reporting this bug.

Also, the new release has updated documentation and tooltips for several of the script's parameters. This should help with ease of use.

 

[Juan Conejero]

I have just released the corresponding updates for MureDenoise 1.22 and its documentation.

Mike, thank you so much for your continued excellent work. Thank you also Adam for your help and support.

[jkmorse]

Mike,

Just a new thank you.  I was struggling using MureDN with my SBIG 6303E but I has recently switched it out for an FLI Microline 16803 and Mure is working beautifully again.  It is just a just a joy using such a well designed script.

Best,

Jim

[mschuster]

Jim,

Thank you, I am glad you are getting better results.

On the SBIG, have you seen significant variation of the median bias level in bias frames? I saw this on my SBIG sometimes. This can make signal and noise harder to distinguish, which can cause trouble in the script.

Mike

[blinky]

I cant get this to make any difference to an Ha image I took with my ASI1600mono.  I have the gain as 200 (that's what was set in SGPro), the offset as o (since it is already calibrated and flat frame subtracted etc) and the noise, I took the 1.2e figure quoted on ZWO website and divided by the Gain (200) but the before & after images look exactly the same, am I doing something wrong?

[mschuster]

blinky,

This "ZWO gain 200" value has dB units, so it is not detector gain, rather it is IMO some sort of camera control parameter.

Looking at the charts on this page astronomy-imaging-camera.com/product/asi1600mm-cool, for "ZWO gain 200", detector gain is about 0.5 e-/DN and detector read noise is about 1.5 e-.

So I suggest for MureDenoise you try values 0.5 e-/DN for detector gain and 1.5 / 0.5 = 3 DN for detector gaussian noise.

As a double check, if you have two bias frames, try using the script DarkBiasNoiseEstimator. Select the two bias frames. The provided "Temporal noise" value is an estimate of detector gaussian noise in DN that you can use in MureDenoise. Of course, it should be about 3 DN assuming your camera is operating as expected.

Also, if you have two well-exposed flat frames (ie, neither underexposed nor overexposed), try using the script FlatSNREstimator. Select the two flat frames, and also one bias frame. The provided "Gain" is an estimate of detector gain in e-/DN which you can use in MureDenoise. Again, assuming everything is as expected the value should be about 0.5 e-/DN. Note it is very important that your flats are well-exposed (if not, garbage in garbage out).

Mike

[blinky]

WOW!  That's better